The present invention relates to a multi-gradation recording method using a printer of the type wherein each one pixel is formed by using each one recording element and the optical density of one pixel formed is represented by the magnitude of the area of the pixel, e.g. printers of various recording systems such as xerography, thermal transfer recording and ink jet recording.
In various recording systems such as xerography, thermal transfer recording and ink jet recording, it is difficult to perform multi-gradation recording according to a density gradation method because it is hard to control the density of pixels to be recorded by toner or ink by itself. Therefore, in such recording systems, a variety of attempts have been made to perform satisfactory multi-gradation recording.
With respect to a method of representing tones, especially intermediate tones by an area gradation method of changing the size of one dot, for instance, in the thermal transfer system, a method of arranging dots to be transferred in the so called zigzag pattern or checkered flag pattern is disclosed in JP, B, 6-59739. It is possible to reproduce satisfactory intermediate tones by the use of this recording method. However, in performing recording in high density region, a large amount of recording energy is required because it is necessary to transfer an ink dot having a larger size than that of a heating resistor of a thermal head. Further, the recording method has the drawback that in performing recording in low density region or high density region, the resultant image has rough appearance and the profile or line of the image is notched due to large clearance between the dots.
Another method of arranging dots to be transferred every other one-dot line, i.e. in a stripe pattern in reproducing intermediate tones is disclosed in JP, B, 7-46828. This method copes with recording in high density region by arranging dots in clearance between the stripes, but the rough appearance or notchy line in low density region is not taken into consideration.
In view of the foregoing, it is an object of the present invention to provide a multi-gradation recording method wherein the recording energy in high density region can be reduced, and the rough appearance in low density region or high density region and notchy appearance in profile or line of the image can be reduced while maintaining the same level of reproduction of intermediate tones as obtained by the conventional recording method using the zigzag pattern or the stripe pattern.
This and other objects of the present invention will become apparent from the description hereinafter.